The present invention relates to a casting apparatus and a casting method for cast-molding a cylinder head of an engine.
As is generally known, a cylinder head of an engine for an automobile engine or the like is provided with paths having complex shapes, such as air-supply and exhaust ports to a cylinder section, paths for engine cooling water (water jackets) and paths for engine oil (oil jackets), and also contains plug holes for ignition plugs corresponding to the number of cylinders and a number of bolt holes used at the time of assembling to a cylinder body; therefore, it has a complex shape as a whole which makes it difficult to apply machining processes such as cutting process, etc., and normally, its base material is therefore obtained as a cast product using an aluminum alloy, etc. as its material.
With respect to a casting method for cast-molding such a cylinder head, a so-called low-pressure casting method has been known in which molten metal inside a stoke is raised by pressing the surface of the molten metal inside a crucible by using compressed air, etc. so that the molten metal thus raised is supplied to a casting mold cavity to be cast (see, for example, Japanese Patent Laid-Open Publication No. 1-53755. In this low-pressure casting method, since the molten metal is pressurized by compressed air, etc., stable high-quality cast products can be obtained, and since virtually no or very little so-called feeder head is required in this method, it is possible to improve the yield of the material to a great degree; thus, this method has various advantages.
Here, in the case when gas such as air is contained in a casting mold cavity to which molten metal is injected to fill, such residual gas inside the cast product tends to cause cast defects such as xe2x80x9cgross porosityxe2x80x9d, etc. In order to prevent the occurrence of such cast defects, it has been well known that an effective method is to give directivity to the cooling process of the molten metal after the casting process so as to allow solidification to start at a portion as far as possible from the gate. By cooling and solidifying the molten metal under such directivity, the residual gas inside the casting mold cavity is gradually driven to the gate side, and finally comes to reside in the gate portion, and in this state, the solidification can be finished. Since the gate portion is cut and removed as a waste portion after completion of the casting process, the possibility of residual gas inside the cast product as it is can be reduced correspondingly, and it becomes possible to effectively reduce the generation of cast defects.
In particular, in the above-mentioned low-pressure casting method, the gate is often formed on the lower mold side of the upper and lower molds, and in this case, gas residing inside the cavity filled with the molten metal is generally allowed to rise to the upper mold side that is far from the gate; therefore, it is essential to carry out the cooling process of the molten metal with directivity in such a manner that cooling of the molten metal is allowed to gradually proceed from the upper mold side farthest from the gate.
Moreover, when the molten metal inside the casting mold cavity is cooled and solidified, the outer side of the casting mold cavity closer to the casting mold surface is generally more susceptible to cooling than the center side thereof due to natural heat radiation outward from the casting mold; therefore, gas tends to reside on the center side of the casting mold cavity. For this reason, with respect to portions on the center side and portions on the outer side of the casting mold cavity as well, it is preferably to carry out the cooling process of the molten metal with directivity in such a manner that cooling of the molten metal is allowed to gradually proceed from the portions on the center side.
In other words, generally in the casting process, in order to improve the productivity, etc., a cooling process is prepared so as to accelerate the solidification of the molten metal upon solidifying the molten metal after the casting process; and in this cooling process, it is essential not only to simply increase the solidifying rate, but also to carry out a cooling process with the above-mentioned directivity.
As described above, in addition to air-supply and exhaust ports, the cylinder head of an engine is provided with passage sections such as the water jackets serving as paths for engine cooling water and the oil jackets serving as paths for engine oil. Therefore, in the case when such a cylinder head is cast-molded, cores corresponding these passage sections are assembled in the casting mold and casting is carried out therein.
When these cores are assembled inside the casting mold, core prints are placed at the ends of each core, and the core is generally assembled in the casting mold through these core prints. Here, in the present specification, xe2x80x9ccore printxe2x80x9d includes to any of those installed integrally with the core main body and those formed on a separate member and used in combination with the core main body.
Among the above-mentioned passage sections, the water jackets and oil jackets are normally placed at parallel upper and lower positions close to each other, after predetermined path cross-sectional areas have been provided respectively within a limited space in the cylinder head.
Therefore, when cores for these two types of jackets are assembled in the casting mold, it is essential to maintain the distance between the axes of the two cores as accurately as possible so as to keep the thickness between the two types of jackets properly.
However, since these two types of jackets are installed in a manner so as to extend virtually over the entire length of the cylinder head in the length direction, the cores have considerably elongated shapes. Therefore, in the case when these cores are respectively assembled in the casting mold independently, it is difficult to stably maintain the distance between the axes of the two types of cores at a fixed value. Moreover, this case results in an increase in the number of the core assembling processes, and also makes the assembling device for the cores more complex, which causes disadvantages in reducing the production costs.
In particular, an arrangement has been proposed in which at least one portion of a casting mold face corresponding to the side face of the cylinder head is formed by an inner side face of a movable side mold that is allowed to slide in a direction (lateral direction) orthogonal to the mold-closing direction of the upper and lower casting molds (for example, Japanese Patent Laid-Open Publication No. 1-53755). However, in the case when such an arrangement is adopted, after the lower-side water jacket core has been set in the lower mold, the upper-side oil jacket core has to be set in the above-mentioned movable side mold.
However, this case raises a problem in which, since a portion of the casting mold that supports the sliding operation of the side mold is subjected to abrasion due to repeated sliding movements, it is difficult to maintain the distance between the axes of the two cores at a fixed value in a stable manner.
Moreover, in order to assemble the lower-side water jacket core of the two types of cores in the lower mold core print stopping portions are formed in portions of the casting mold corresponding to core prints on the two ends of the water jacket core, and engaging sections that engage the core print stopping portions are formed in the respective core print sides; thus, positioning and securing operations are generally carried out by allowing the engaging sections to engage the corresponding core print stopping portions.
However, in such a conventional arrangement, since the respective engaging sections are set in their shape and dimension so as to engage the core print stopping portions in a manner so as not to move in any directions in order to prevent positional offsets of the core, the core is secured in a completely rigid manner by the core print portions on the two ends. This arrangement tends to raise another problem in which, when, upon casting, molten metal is injected in the casting mold cavity so as to fill it, the core is susceptible to cracks and chips due to differences in the amount of thermal expansion between the metal casting mold and the core having casting sand as its main material
Moreover, another arrangement has been proposed in which, instead of assembling the two types of cores for water jackets and oil jackets independently in the casting mold, the two cores are preliminarily assembled integrally, and these pre-assembled cores are assembled in the casting mold. However, even in this arrangement, the core is susceptible to cracks and chips due to differences in the amount of thermal expansion caused by temperature differences, etc. between the cores.
Moreover, as has been well known, the respective cores are formed by using casting sand as its main material with which a binder having resin as its main component is blended, and in this case, when such a core is assembled in the casting mold and subjected to a casting process, the binder contained in the core is gasified due to heat of the molten metal, and the residual gas inside the cast product tends to cause so-called gas defects. Therefore, in the casting process, it is essential to discharge such gas outside the casting mold quickly before the solidification of the molten metal.
However, since the water jacket core and the oil jacket core have elongated shapes as described earlier, it is difficult to discharge the gas generated inside thereof quickly outside the casting mold.
Here, in this case also, in order to prevent the generation of cast defects such as xe2x80x9cgross porosityxe2x80x9d, etc, due to residual gas such as air inside the cast product, it is effective to give directivity to the cooling process of the molten metal after the casting process so as to allow solidification to start at a portion as far as possible from the gate. In particular, in the above-mentioned low-pressure casting method, it is more important to carry out the cooling process of the molten metal with such directivity.
In this case, it is very preferable if such directivity in the cooling process can be achieved by utilizing the core that more hardly transmits heat as compared with the metal casting mold, because of its main material of casting sand.
As has been well known, in the case when a cast product is obtained by injecting molten metal into a volume section formed between casting molds placed face to face with each other, in order to distribute the molten metal smoothly over the inner face of the casting molds, or in order to take the cast product after the solidification of the molten metal out of the casting mold smoothly, it is a general method to preliminarily apply a mold wash to the inner face of the casting mold, prior to a casting process.
For example, in the above-mentioned low-pressure casting method, since, in most cases, the gate is formed on the lower mold side of the upper and lower molds; consequently, in order to maintain a better molten-metal distributing property on the upper mold side that is susceptible to a temperature drop in the molten metal temperature, it is particularly essential to properly apply a mold wash to the inner face of the upper mold.
Moreover, in general, when, upon completion of a casting process, the upper mold is raised to open the molds, a resulting cast product is also raised together with the upper mold; therefore, it is necessary to separate the cast product from the upper mold. In this case, if the mold-releasing properly is poor, it is necessary to increase a pushing force of the ejector pin, and this makes the ejector mechanism bulky, and might cause damages to the resulting cast product. Therefore, from this viewpoint also, it is essential to properly apply a mold wash to the inner face of the upper mold.
In relation to the application method of a mold wash to the inner face of the casting mold (upper mold) in the low-pressure casting method, the applicant, etc. of the present application has proposed a coating method in which, upon application of a powder mold wash to the inner face of the upper mold, the mold wash, which has dropped without sufficiently adhering to the inner surface of the upper mold, is again allowed to adhere to the inner face of the upper mold so that the adhering efficiency of the mold wash is improved so as to provide an appropriate application process (see Japanese Patent Laid-Open Publication No. 9-225589).
Here, for example, in the case of a casting process for a cylinder head for an automobile, a plurality of side wall portions, which form casting mold faces corresponding to the side faces of the cylinder head, are installed in addition to a pair of upper and lower molds. In the cylinder head casting apparatuss in relation to the above-mentioned patent publications, these wall portions are formed as sand walls on the lower mold side; however, it has been well known in the art that these side wall portions are formed as molds, that is, as movable side wall casting molds that are slidable in a direction (lateral direction) virtually orthogonal to the opening and closing directions (up and down directions) of the upper and lower main casting molds.
In this arrangement in which the side wall portions are provided as the movable side wall casting molds slidable in the lateral direction, in general, all the movable side wall casting molds or at least one portion thereof (for example, in the case of four faces of the side wall portions, the side wall casting molds corresponding to, a least, two faces thereof) are arranged so as to be supported on the lower mold side.
However, in the case when the side wall casting molds are arranged in this manner, upon application of a mold wash, the coating process to the inner faces of the side wall cast molds has to be carried out in a separate manner from the inner face of the upper mold, and the coating process has to be conducted twice (that is, in two processes); this causes degradation in the efficiency of the process.
Moreover, upon application of the mold wash to the inner faces of the casting molds, it is essential to ensure a proper adhering property (contacting property) of the mold wash to the inner faces of the casting molds. Here, since the adhering property of the mold wash is influenced by the temperature of the casting mold, it is essential to properly control the casting mold temperature at the time of coating.
Furthermore, as described earlier, for example, upon carrying out the casting process for a cylinder head, after the cores corresponding to passage sections such as air-supply and exhaust ports to the cylinder section, paths for engine cooling water (water jacket) and paths for engine oil ,(oil jackets) have been assembled in the casting mold, the casting process is carried out, and these assembling process for the cores and the coating process of the mold wash are both carried out on the casting mold.
Therefore, in the case when the coating process of the mold wash and the assembling process for the cores are commonly carried out on the casting mold, it is important to carry out both of the processes in a properly synchronized timing so as to improve the production efficiency in the casting process as a whole.
Accordingly, the objectives of the present invention are basically described as follows: Upon cast-molding a cylinder head for an engine, a proper directivity is given to the cooling process of the molten metal after the casting process by utilizing the shape of the cylinder head so as to obtain high-quality cast products, and the distance between the axes of the two elongated cores is accurately maintained so as to prevent damage to the cores or so as to quickly discharge gas generated inside the cores out of the casting mold; thus, it is possible to reduce gas defects in the resulting cast mold. Moreover, upon application of the mold wash to the inner face of the casting mold provided with movable side wall casting molds, the efficiency of the coating process is improved, and the adhering property of the mold wash to the inner face of the casting mold is improved, or, when the coating process of the mold wash and the assembling process of the cores are carried out together, the production efficiency of the casting process as a whole is enhanced.
In order to achieve the above object, in a first aspect of the present invention, there is provided a casting apparatus of a cylinder head, which comprises a pair of upper and lower molds that are separably joined to each other and which cast-molds a cylinder head of an engine by injecting molten metal into a casting mold cavity formed between the two molds so as to fill it with the molten metal to be solidified, through a gate formed in the lower mold, wherein a plurality of core protrusions corresponding to holes are formed on the upper mold with cooling means being attached to each of the core protrusions, the cooling means attached to inner core protrusions comparatively closer to the center of the mold being designed so as to have a greater cooling capability than those attached to outer core protrusions comparatively closer to the periphery of the mold.
In a second aspect of the present invention, there is provided a casting apparatus of a cylinder head as described in the first aspect, wherein a cooling medium of the cooling means attached to the inner core protrusions is liquid and a cooling medium of the cooling means attached to the outer core protrusions is gas.
Further, in a third aspect of the present invention, there is provided a casting apparatus of a cylinder head as described in the second aspect, wherein a removing means is installed so as to remove residual cooling medium inside the core protrusions after stoppage of the cooling operation of the cooling means attached the inner protrusions.
Still further, in a fourth aspect of the present invention, there is provided a casting apparatus of a cylinder head as described in the first aspect, wherein the core protrusions correspond to at least a plug hole located comparatively closer to the center of the cylinder head and a bolt hole located comparatively closer to the periphery of the cylinder head.
Still further, in a fifth aspect of the present invention, there is provided a casting apparatus of a cylinder head. as described in the first aspect, wherein side walls are provided so as to form a casting mold cavity with the upper and lower molds, and a spot cooling means, which restricts thermal conduction so as not to be exerted in any direction other than a specific direction, is installed at least in either the upper or lower mold.
Still further, in a sixth aspect of the present invention, there is provided a casting apparatus of a cylinder head as described in the first aspect, wherein first and second elongated cores are to be assembled in a mold before molten metal is injected into a casting mold cavity, wherein core prints are placed on both ends of each of the two cores; the first core is assembled in the casting mold through the core prints; and the second core is assembled in the casting mold with core prints thereof being supported by the core prints of the first core.
Still further, in a seventh aspect of the present invention, there is provided a casting apparatus of a cylinder head as described in the sixth aspect, wherein a suction means is installed so as to suck, through at least either of the core prints of the two cores, gas generated in the core or the other core at the time of a casting process.
Still further, in an eighth aspect of the present invention, there is provided a casting apparatus of a cylinder head as described in the first aspect, wherein side wall casting molds which form the side walls are supported by the upper mold; a mold cooling means is installed on the upper mold so as to cool the mold in accordance with the temperature thereof; the side wall casting molds are installed in a manner so as to be switched between a mold-closed state for forming a sealed volume section and a mold-opened state for allowing the volume section to open; and under conditions that all the side wall casting molds are set in the mold-closed state and that the upper mold is cooled to a temperature in a predetermined temperature range, a mold wash is applied to inner faces of the side wall casting molds and the upper mold.
Still further, in a ninth aspect of the present invention, there is provided a casting apparatus of a cylinder head, which comprises a pair of upper and lower molds that are separably joined to each other and side walls, and which cast-molds a cylinder head of an engine by injecting molten metal into a casting mold cavity formed by the two molds and the side walls so as to fill it with the molten metal to be solidified, through a gate formed in the lower mold, wherein a spot cooling means, which restricts thermal conduction so as not to be exerted in any direction other than a specific direction, is installed at least in either the upper or lower mold.
Still further, in a tenth aspect of the present invention, there is provided a casting apparatus of a cylinder head as described in the ninth aspect, wherein the spot cooling means is formed by installing a cooling medium path inside a cylindrical member, the cylindrical member having one end face facing the inside of the casting-mold cavity and a peripheral portion being fitted to a mounting hole formed in the mold.
Still further, in an eleventh aspect of the present invention, there is provided a casting apparatus of a cylinder head as described in the ninth aspect, wherein one portion of the side walls is formed by a sand wall, with the spot cooling means being installed in the vicinity of the sand wall.
Still further, in a twelfth aspect of the present invention, there is provided a casting apparatus of a cylinder head as described in the ninth aspect, wherein: a molten metal supply section for supplying the molten metal to be injected into the casting mold cavity through the gate is installed below the lower mold; a predetermined space is formed between the molten metal supply section and the lower mold; a cooling medium path for the spot cooling means is placed in the space; and a communicating path for allowing the molten metal supply section to communicate with the gate is formed therein.
Still further, in a thirteenth aspect of the present invention, there is provided a casting apparatus of a cylinder. head, which comprises a pair of upper and lower molds that are separably joined to each other and side walls, and which cast-molds a cylinder head of an engine by injecting molten metal into a casting mold cavity formed by the two molds and the side walls so as to fill it with the molten metal to be solidified, through a gate formed in the lower mold, wherein a plurality of core protrusions corresponding to holes are formed on the upper mold with cooling means being attached to each of the core protrusions, the cooling means attached to inner core protrusions comparatively closer to the center of the mold being designed so as to have a greater cooling capability than those attached to outer core protrusions comparatively closer to the periphery of the mold, and in that a spot cooling means, which restricts thermal conduction so as not to be exerted in any direction other than a specific direction, is installed in the lower mold.
Still further, in a fourteenth aspect of the present invention, there is provided a casting method for a cylinder head, which comprises the steps of preparing a pair of upper and lower molds that are separably joined to each other and cast-molding a cylinder head of an engine by injecting molten metal into a casting mold cavity formed between the two molds so as to fill it with the molten metal to be solidified, through a gate formed in the lower mold, wherein a plurality of core protrusions corresponding to holes are formed on the upper mold with cooling means being attached to each of the core protrusions, the cooling means attached to inner core protrusions comparatively closer to the center of the mold being designed so as to have a greater cooling capability than those attached to outer core protrusions comparatively closer to the periphery of the mold.
Still further, in a fifteenth aspect of the present invention, there is provided a casting method for a cylinder head as described in the fourteenth aspect, wherein side walls are provided so as to form a casting mold cavity with the upper and lower molds, and a spot cooling means, which restricts thermal conduction so as not to be exerted in any direction other than a specific direction, is installed at least in either the upper or lower mold.
Still further, in a Sixteenth aspect of the present invention, there is provided a casting method for a cylinder head as described in the fourteenth aspect, wherein first and second elongated cores are to be assembled in a mold before molten metal is injected into a casting mold cavity, wherein core prints are placed on both ends of each of the two cores; the first core is assembled in the casting mold through the core prints; and the second core is assembled in the casting mold with core prints thereof being supported by the core prints of the first core.
Still further, in a seventeenth aspect of the present invention, there is provided a casting method for a cylinder head as described in the sixteenth aspect, wherein a suction means is installed so as to suck, through at least either of the core prints of the two cores, gas generated in the core or the other core at the time of a casting process.
Still further, in an eighteenth aspect of the present invention, there is provided a casting method for a cylinder head as described in the fourteenth aspect, wherein side wall casting molds which form the side walls are supported by the upper mold; a mold cooling means is installed on the upper mold so as to cool the mold in accordance with the temperature thereof; the side wall casting molds are installed in a manner so as to be switched between a mold-closed state for forming a sealed volume section and a mold-opened state for allowing the volume section to open; and under conditions that all the side wall casting molds are set in the mold-closed state and that the upper mold is cooled to a temperature in a predetermined temperature range, a mold wash is applied to inner faces of the side wall casting molds and the upper mold.
Still further, in a nineteenth aspect of the present invention, there is provided a casting method for a cylinder head, which comprises the step of preparing a pair of upper and lower molds that are separably joined to each other and side walls, and which cast-molds a cylinder head of an engine by injecting molten metal into a casting mold cavity formed by the two molds and the side walls so as to fill it with the molten metal to be solidified, through a gate formed in the lower mold, wherein a spot cooling means, which restricts thermal conduction so as not to be exerted in any direction other than. a specific direction, is installed at least in either the upper or lower mold.
Still further, in a twentieth aspect of the present invention, there is provided a casting method for a cylinder head , which comprises the step of preparing a pair of upper and lower molds that are separably joined to each other and side walls, and which cast-molds a cylinder head of an engine by injecting molten metal into a casting mold cavity formed by the two molds and the side walls so as to fill it with the molten metal to be solidified, through a gate formed in the lower mold, wherein a plurality of core protrusions corresponding to holes are formed on the upper mold with cooling means being attached to each of the core protrusions, the cooling means attached to inner core protrusions comparatively closer to the center of the mold being designed so as to have a greater cooling capability than those attached to outer core protrusions comparatively closer to the periphery of the mold, and in that a spot cooling means, which restricts thermal conduction so as not to be exerted in any direction other than a specific direction, is installed in the lower mold.